Studies on endogenous sequences of FeLV and RD114: Determine the sites of integration of FeLV and RD114 related sequences by transferring individual cat chromosomes to a mouse background; and testing for the presence of the proviral sequences in situ and other molecular hybridization tests. Map the provirus in relation to other markers in the cat genome. Studies on exogenous FeLV: Conduct somatic cell hybrids between mouse and exogenously infected cat cells, and test the synteny of the exogenous FeLV sequences with specific chromosomes and marker genes. Prepare hybrids of mouse x Asian cat (Felis viverrina) tissue culture cells infected with FeLV+ cat chromosomes free of endogenous FeLV sequences. Test for integration site of exogenous FeLV.